1. Field of the Invention
The present invention relates to a combination weighing device combining objects having different weights with each other to reach a prescribed weight. More specifically, it relates to a technique of controlling the quantity of objects in a combination weighing device.
2. Description of the Background Art
In order to bag objects such as sweets or vegetables having different weights by a prescribed weight, a combination weighing device is employed for temporarily grouping the objects, measuring the weights of the groups and selecting a combination of groups exhibiting a total weight corresponding to the prescribed weight.
Briefly stated, a cross feeder of a general combination weighing device supplies objects to a dispersion feeder. The dispersion feeder dispersively discharges the supplied objects to a plurality of radiation feeders, which in turn introduce the objects into pool hoppers. The combination weighing device treats the objects introduced into each pool hopper as a group, and introduces the same into a measuring hopper every group. Each measuring hopper measures the weight of the group transported from the corresponding radiation feeder, and outputs the result of the measurement to a control part consisting of a CPU or the like. The control part selects the optimum combination of measuring hoppers storing objects exhibiting a total weight corresponding to a prescribed weight on the basis of the results of measurement received from the measuring hoppers and instructs the selected measuring hoppers to introduce the groups stored therein. The measuring hoppers instructed by the control part open on-off gates for introducing the groups into a collecting chute. The combination weighing device bags the plurality of groups introduced into the collecting chute through a discharge chute. In such a combination weighing device, the probability of presence of the optimum combination depends on how to control the weight of the group introduced into each measuring hopper.
Therefore, generally proposed is a combination weighing device controlling the manipulated variable for each radiation feeder thereby controlling the weight of a group of objects transported to each measuring hopper. For example, this combination weighing device previously sets the number of measuring hoppers introducing objects in one cycle among a plurality of measuring hoppers. In an initial state of operations or when no proper combination is obtained, the combination weighing device automatically controls the manipulated variable for each radiation feeder so that the weight of the group of objects introduced into each measuring hopper reaches an ideal weight (obtained by dividing a prescribed weight by the number of measuring hoppers introducing objects) of objects introduced by a single measuring hopper.
In such a combination weighing device, however, the weights of groups of objects introduced into the respective measuring hoppers may unidirectionally fluctuate due to fluctuation of a power supply line or unidirectional fluctuation of supplied states for the respective radiation feeders. When the combination weighing device controls the quantities of introduction into all measuring hoppers to reach the ideal weight as described above in this case, the objects introduced into all measuring hoppers exceed the ideal weight and the total weight of bagged objects exceeds a prescribed weight whichever measuring hoppers are combined with each other, for example. In other words, the probability of presence of combinations exhibiting quantities of bagged objects reaching a target measured value is remarkably reduced under this control when the aforementioned fluctuation takes place.
Therefore, proposed is a device controlling each radiation feeder to disperse the weight of a group of objects introduced into each measuring hopper about an ideal weight thereby maintaining the probability of presence of combinations when the aforementioned fluctuation takes place.
However, while the aforementioned device can deal with fluctuation of supplied states or the like, standard deviation of the weights of groups of objects introduced into respective measuring hoppers in a general state is so large that the probability of presence of combinations itself is disadvantageously low.
When the quantity of objects supplied to each radiation feeder is increased, there is a high possibility that an overscale state takes place in a measuring hopper corresponding to a radiation feeder having a relatively largely set manipulated variable since the radiation feeder is originally controlled to disperse the quantity of introduction.
When the overscale state takes place in the measuring hopper, the weight of a group of objects introduced into this measuring hopper is in excess of a target measured value, and the measuring hopper is unusable in this case.